MELBOURNE - Wild storms lashing Australia forced police to warn people to stay away from the centre of the country's second most populous city on Thursday after Melbourne experienced its heaviest rainfall in almost 150 years.

A teenage girl was killed by a falling tree in the state of New South Wales as the unseasonal storms swept southeastern Australia and the mercury plummeted in the middle of summer causing snow to fall in the mountains.

Victorian police urged people to avoid unessential travel into the centre of Melbourne, which was soaked by 120 mm (5 inches) of rain overnight, after flash flooding, power blackouts and fallen trees wreaked havoc with traffic and public transport.

Thousands of homes in Victoria, New South Wales, Tasmania and Queensland lost power and strong winds ripped roofs from homes as an intense low pressure system moved slowly across the states bringing some of the coldest February weather on record.

"Whenever you are talking about records (being broken) you have got to say its unusual. We would characterise this typically as a winter-time pattern," Bureau of Meteorology Senior Forecaster Jon Gill told Reuters.

On Tuesday,the mercury hit 36 degrees Celsius (97 degrees Fahrenheit) in Melbourne, but could barely reach a high of 13 degrees Celsius on Wednesday.

The weather forced flights to be diverted away from Melbourne on Wednesday night and the Yarra River, which runs through the centre of the city, burst its banks in several places.

But Gill said it was too early to tell whether the rain was enough to break Australia's worst drought in a century.

"Given the very large areas that have experienced very substantial rainfalls, this will certainly help the catchments a great deal so I think it's good news. But it's a little bit early to say just how much the dams will fill up," Gill said.

There were no signs of the weather abating on Thursday as rain continued to fall across southeastern Australia.